Angry Birds: Crows Never Forget Your Face

Crows remember the faces of threatening humans and often react by scolding and bringing in others to mob the perceived miscreant, according to a new study published in the latest Proceedings of the Royal Society B.

Since the mob members also then indirectly learn about the threatening person, the findings demonstrate how just a single crow's bad experience with a particular human can spread information about this individual throughout entire crow communities.

Given that crows have impressive memories, people who ruffle the feathers of these birds could experience years of retribution.

Bothered crows may at first "give harsh calls, which we call 'scolds' that attract other crows who are nearby to join in the mob," according to study co-author John Marzluff. "The mob of two to 15 birds hounds us, sometimes diving from the sky to within a few meters or less -- This pursuit lasts about 100 meters (328 feet) as we walk away."

Marzluff is a professor at the University of Washington's School of Forest Resources. For the study, he and colleagues Heather Cornell and Shannon Pecoraro exposed wild crows to a novel "dangerous face" by wearing a unique mask as they trapped, banded and released seven to 15 birds at five study sites near Seattle.

The released birds immediately scolded the mask wearer. Hearing the racket, other crows joined, forming an angry mob.

When the researchers later put on other masks while traveling to different areas, crows that were never captured immediately recognized the "dangerous face," illustrating how these birds learned through social means and not as a result of direct experience. Both relatives and strangers joined in the scolding and mobbing, which could occur over a mile away from the original incident.

Once such a face is locked into a crow's memory, it's likely there for good.

"Our study shows the memory lasts at least five years and counting," Marzluff said. "Individual crows that are adults can live 15-40 years in the wild (most die when young, but those that make it to adulthood can live a long time) and they probably remember important associations they have formed for much of their lives."

Prior research demonstrates that crows are particularly intelligent birds.

"Others have shown that some crows make and use tools, forecast future events, understand what other animals know, and -- in our case -- learn from individual experience as well as by observing parents and peers," Marzluff explained. "These are all advanced cognitive tasks shown by only a few animals."

He suspects other social, long-lived species that live closely with humans might also share information in a similar manner. Possibilities include animals such as coyotes, raccoons, gulls, pigeons and rats. All could practice a combination of social and trial and error learning. The latter provides the most accurate information, but it is clearly riskier than indirect social learning.

In the animal kingdom, humans have a language advantage because we can just verbally warn others about dangers. Vocalizations do not appear to be enough for crows, which appear to require visual observation for the information to sink in.

Anne Clark, an associate professor in the department of Biological Sciences at Binghamton University, told Discovery News that this new study "suggests importantly how much long-term studies of individuals have to contribute to our understanding of adaptive social learning."

She added, "I doubt that anyone working with crows will be surprised by the results suggesting several routes of social transmission, but this kind of formal, empirical testing is much needed."

Kevin McGowan, an instructor at the Cornell Lab of Ornithology, echoed Clark's comments, but said the findings might surprise "anyone who thinks animals only learn by direct experience."

"Social animals are social for lots of very good reasons," McGowan continued. "This study demonstrates one of the more subtle ways that animals benefit from interactions with other members of their own species."

Animal tool use is far more common than previously thought, with fish recently added to the animal tool wielder's list. Here, a green wrasse picks up a clam. The fish later uses a rock as an anvil to smash open the clam.
Such underwater cleverness should come as no surprise, according to Culum Brown, director of advanced biology at Macquarie University. "Fish are always ignored when it comes to cognition," he told Discovery News. "That is largely due to our self-centered view of evolution. But even ignoring that bias, we would still seldom study fish because they are simply hard to observe."
Added Brown, whose findings are outlined in the latest issue of the journal Fish and Fisheries, "I'm sure tool use is far more common in fish than we realize."

Fish aren't the only underwater tool users. Dolphins break off sponges and wear them, but it's likely not a fashion statement.
"We believe that the marine sponge acts as a kind of glove to protective their sensitive rostra," marine biologist Michael Krützen of the University of Zurich told Discovery News.
"That probing (of the sea floor) might disturb fish that hide in the sand, which would then be easy targets for the dolphins."

Brown believes that "many animals resort to tool use when they lack the physical capability to access a resource, nearly always food, without the specific aid of a tool."
This photo shows a selection of sticks altered by chimpanzees at Kibale Forest National Park in Uganda to get at honey and other food.

Animals may use tools for defense, as does this decorator (also sometimes called "dresser") crab.
The crab possesses Velcro-like hooks on its shell that hold "accessories," which in this case are living coral polyps and sea anemones.
The other creatures give the crab a bottom-of-the-sea look that helps to disguise it on the reefs where it lives.

The closer animals are to our own species, the more their tool usage seems human-like.
This adult female gorilla named Leah from Nouabalé-Ndoki National Park in northern Congo, turned a big branch into a multi-purpose tool.
She used it as a walking stick, for postural support, and to test both the substrate and the water depth. Leah proves three aspects of animal tool usage highlighted by Brown.
"First, the animal has to be in an environment where suitable tools are available," he said. "Second, the animal has to have the physical and mental capacity to use the tool. Third, the physics of the environment make tool-use possible."
For the latter, he points out that fish don't have hammers because swinging them underwater "is really hard work and not very effective."

Tools don't always provide the fastest, easiest solution to problems.
In the case of New Caledonian crows, for example, their use of sticks to dislodge wood-boring beetle grubs from rotting tree trunks requires a lot of time and practice. Why do crows even bother with the sticks then?
Christian Rutz of the University of Oxford and colleagues investigated the benefits of this tool use by analyzing how different types of food contribute to individual crow diets.
As it turns out, just a few beetle larvae pulled out by sticks can satisfy a crow's daily energy requirements. So all of the extra effort is worth it.

Sometimes tools can aid in sudden life or death matters.
This small octopus from East Timor was seen on a night dive hiding between a nutshell and a clamshell.
When things got quiet, the octopus snuck out, carrying the shells. Sensing threats, it then clamped itself back between the portable hideout.

One of the most unusual animal tools is a "kiss squeak toy" that orangutans construct out of leaves.
Madeleine Hardus of the Behavioral Biology Group at the University of Utrecht told Discovery News that the resulting noise is hardly a love call. Instead, orangutans produce it when predators startle them, or they are otherwise disturbed.
"As far as I and my colleagues know, no other primate emits kiss squeak sounds," Hardus said.
"Male great apes can use their hands during the production of calls, such as buttress-drumming in chimpanzees, chest-beating in gorillas and snag-crashing in orangutans, but in these examples, calls are not modified; they're added with other acoustic elements. Only kiss squeaks are known to be modified."

It may not be pretty, but mammal dung serves as a useful tool for burrowing owls.
The owls collect the dung and spread it around the entrance to their homes, as seen here. Dung-consuming beetles find the bait irresistible. As the beetles are investigating the fragrant balls, the owl comes out for its crunchy bug dinner.

Our human ancestors were using stone tools and eating meat from large mammals nearly a million years earlier than previously thought, according to a Nature study that pushed back both of these human activities to around 3.4 million years ago.
The first known human ancestor tool-wielder and meat-lover was Australopithecus afarensis, according to the study. This species, whose most famous representative is the skeleton "Lucy," was slender, toothy and small-brained.
"By pushing the date for tool use and meat-eating in our lineage back by around 1 million years, our finds show that tool use and meat-eating was not unique to (the genus) Homo," co-author Zeresenay Alemseged told Discovery News.
"Also, by showing that A. afarensis was involved in these activities, we showed that you do not need a large brain to do this," added Alemseged, director of the Department of Anthropology at the California Academy of Sciences.
Brown agrees that braininess may not always explain how much or little certain species use tools.
"Are there physical and or ecological constraints on tool use?" he said. "Hopefully if we do this we can get away from the notion that 'humans use tools so tool-users must be smart like humans.' That idea seems to be leading us in circles."